Stratified composite with phosphorescent properties, method for the production and the use thereof

ABSTRACT

Laminar body comprising a substrate and, applied thereto on one or both sides, at least one layer containing an enamel, wherein the layer or layers containing an enamel contains/contain at least one phosphor.

The present invention relates to a laminar body comprising a substrateand, applied thereto on one or both sides, at least one layer containingan enamel, wherein the layer contains at least one phosphor. Such alaminar body has phosphorescent properties. The present invention alsorelates to a process for producing the above-defined laminar body, toits use for giving phosphorescent properties to an article providedtherewith and to these articles themselves.

The laminar body of the invention can be used wherever a situationdangerous to people can arise as a result of sudden failure of generallighting. This can be achieved in the form of markings and safety signsin the context of a safety guidance system possessing persistentphosphorescence in order to lead persons safely along a prescribedescape route to an exit or to a safe area.

Processes for producing steel enamel having persistent phosphorescenceare known. Steel enamels having persistent phosphorescence have hithertobeen produced using phosphors based on zinc sulphides.

In order to be able to achieve certain minimum phosphorescence values, arelatively thick phosphor-containing enamel coating had to be chosen.These processes allow no technical possibility of enameling thin,flexible and thus more or less universally usable substrates, e.g. foilsbased on aluminum or aluminum alloys.

An attempt to lower the thicknesses of the enamel layer by use oflaminated films led only to laminar bodies which are partly combustibleor thermally decomposable. Such laminar bodies having persistentphosphorescence display good phosphorescence values but have thedecisive disadvantage of thermal decomposability. This thermaldecomposition of plastics is always associated with the liberation ofirritating and toxic gases and therefore makes such laminar bodiesunusable for a series of applications.

It was therefore an object of the present invention to produce laminarbodies which have good phosphorescence properties, are preferably notcombustible and do not liberate any irritating or toxic gases under theaction of heat. Furthermore, these laminar bodies should be able to beproduced in any configuration by screen printing or else by otherprinting processes.

In addition, the laminar bodies should be inexpensive to produce, beusable and be replaceable without problems.

These and further objects are achieved by the laminar body of theinvention.

The present invention accordingly provides a laminar body comprising asubstrate which preferably contains aluminum or an aluminum alloy and,applied thereto on one or both sides, at least one layer containing anenamel, characterized in that the enamel layer or layerscontains/contain a phosphor.

If complete noncombustibility in use is necessary, the laminar body ofthe invention can be constructed so as to be free of plastics.

As substrate in the laminar body of the invention, it is possible to useany substrates which can be enameled, in particular those based onmetals, e.g. ferrous materials, materials containing aluminum or analuminum alloy, copper-, silver-, gold- and titanium-containingmaterials. Preference is given to using a substrate which containsaluminiium or an aluminum alloy.

Although the thickness and structure of the substrate are subject to noparticular restrictions, preference is given to using perforated metalsheets having a thickness of from about 0.2 to about 2.5 mm, morepreferably from about 0.5 to about 2.0 mm and in particular from about0.5 to about 1.5 mm, or foils having a thickness of from about 50 toabout 500 μm, more preferably from about 100 to about 400 μm and inparticular from about 200 to about 300 μm. There is virtually norestriction in respect of the free perforation area of the perforatedmetal sheets, but preference is given to using perforated metal sheetshaving a free perforation area of from about 20 to about 45%.

For the purposes of the present invention, it is in principle possibleto use as substrate all known aluminum alloys in which the mostimportant alloying constituents are, for example, copper, magnesium,silicon, manganese and zinc and also mixtures of two or more thereofand, in smaller amounts, nickel, cobalt, chromium, vanadium, titanium,lead, tin, cadmium, bismuth, zirconium and silver and also mixtures oftwo or more thereof.

In addition, the laminar body of the invention comprises a layer whichcontains an enamel and is applied to either one or both sides of theabove-defined substrate.

For the purposes of the present application, the term “enamel”corresponds to the definition given in “Email und Emailliertechnik”,Petzold/Pöschmann, Deutscher Verlag fair Grundstoffindustrie,Leipzig/Stuttgart, 2nd revised edition 1992, page 15. Accordingly,enamel is a preferably vitreous, solid material formed by melting orfritting and having an inorganic, mainly oxidic-siliceous compositionwhich is to be melted or has been melted in one or more layers,sometimes together with additives, onto metal workpieces.

The enamel used according to the invention can be produced from anenamel frit which contains heavy metals or is free of heavy metals.

Here, the term “free of heavy metals” means that the enamel frit used iscompletely or essentially free of metals which have an atomic numbergreater than the atomic number of calcium.

In a preferred embodiment of the present invention, in which thesubstrate contains aluminum or an aluminum alloy, enameling is carriedout using an aluminum enamel. With regard to this, the following needsto be noted. The low melting point of aluminum and its alloys demandsenamels which can be fired at from about 520° C. to 560° C. Thiscorresponds to a softening temperature of about 450° C. Accordingly, thestarting materials employed in this embodiment are enamel frits whichhave the abovementioned properties.

This can be achieved using, for example, glasses having a high contentof Li₂O, BaO and V₂O₅. Eutectics containing fluoride or enamels based onphosphate also meet the temperature requirement. Although theabovementioned conditions in respect of the softening point can beachieved by addition of these constituents, preference is given toadding further constituents to increase the chemical resistance of theresulting enamel. Thus, for example, good values for the resistance ofthe resulting enamel to aggressive media can be achieved by changing theratios of Li₂O and TiO₂ and the contents of alkaline earth metal andZnO. Details on this subject may be found in Migonadziev, A. S., Stekloi keramika (1966), 12, p. 15.

Aluminum enamels can be produced in all colours and also in black andwhite. In the case of the white enamels, opacifiers such as TiO₂ areadded and an appropriately high ratio of Li₂O to TiO₂, i.e. about1:1.5-2, then has to be selected. Coloured aluminum enamels can beproduced in many shades.

By way of example, the composition of an enamel which is very useful forthe purposes of the invention will once more be described here:

100 parts of frit

15 parts of phosphorescent pigment

4 parts of boric acid

2 parts of KOH

1 part of water glass

45 parts of water

This mixture is milled in a porcelain mill to give a slip having adefined particle fineness of, for example, from 0.1 to 0.5 by the Bayermethod and a specific gravity of, for example, from 1.5 to 2.0 g/cm³,preferably from 1.7 to 1.8 g/cm³.

This slip is usually applied to the part to be enameled by a sprayingmethod.

Further details of such aluminum enamels or the enameling of substratescontaining aluminum or aluminum alloys may be found, for example, in areview article “Mitteilungen des Vereins Deutscher Emailfachleute e.V.”,volume 43, 1995 (No. 5), p. 56 ff.

The thickness of the enamel layer or layers is preferably 400 μm orless, more preferably about 300 μm or less and in particular about 200μm or less, with the lower limit of the thickness of the enamel beingabout 30 μm.

In a further, preferred embodiment, a reflective layer of a white orlight-coloured enamel having a reflectance of at least about 78%, morepreferably at least about 82%, is first applied on one or both sides andat least one further enamel layer is then applied.

Furthermore, a reflective layer can also be produced directly on thesubstrate, for example by electric oxidation and/or by embedding ofinorganic pigments such as TiO₂.

Of course, the enamel containing a phosphor can also be applied directlyto the substrate without using a reflective layer.

If more than one layer containing an enamel is applied to one or bothsides, it is advantageous, particularly for economic reasons, for onlythe outer layer containing an enamel to contain a phosphor.

Phosphors which can be used for the purposes of the present inventionare in principle all known inorganic phosphors.

Examples which may be mentioned are:

Phosphors as are described, for example, in Ullmanns Encyklopädie derTechnischen Chemie, 4th edition, volume 16, p. 179 ff (1975), e.g. thosebased on sulphides, e.g. CaS:Bi, CaSrS:Bi, ZnS:Cu and ZnCdS:Cu;

phosphors based on alkaline earth metal aluminates, e.g. europium- orlead-activated alkaline earth metal aluminates, where the alkaline earthmetal is strontium or a mixture of strontium and calcium, as described,for example, in EP-A-0 094 132 and U.S. Pat. No. 3,294,699 (Sraluminate/europium), likewise europium-activated alkaline earth metalaluminates containing barium and strontium as alkaline earth metals, asdescribed in DE-A-1 811 732;

phosphors comprising a matrix of the formula M_(1−x),Al₂O_(4−x), where Mis at least one metal selected from among Ca, Sr and Ba and x is anon-zero integer and the matrix contains Eu as activator and, ascoactivator, at least one of La, Ce, Pr, Nd, Sm, Gd, Th, Dy, Ho, Er, Tm,Yb, Lu, Mn, Sn and Bi, as described in EP-A-0 710 709;

phosphors comprising a composition MO˜a(Al_(1−b)B_(b))₂O₃:cR, where0.5≦a≦10.0, 0.0001≦b≦0.5 and 0.0001≦c≦0.2, MO is at least one divalentmetal oxide selected from among MgO, CaO, SrO and ZnO, and R is Eu andat least one additional rare earth element, as described in DE-A 195 21119;

alkaline earth metal aluminates doped with rare earth metals, asdescribed in EP-A-0 710 709 and DE-A 195 21 119;

phosphors comprising a matrix of the formula MAl₂O₄, where M is calcium,strontium or barium and the matrix contains europium as activator and,as coactivator, at least one of lanthanum, cerium, praseodymium,neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium, tin and bismuth, as described in EP-B-0 622 440;

europium-activated ternary metal oxides containing SrO or BaO ormixtures thereof, Al₂O₃ or a mixture of Al₂O₃ and Ga₂O₃ and ZnO or MgO,as described in U.S. Pat. No. 4,216,408;

and phosphors containing at least one metal oxide selected from amongMgO, CaO, SrO and ZnO, and also, as activator, Eu²⁺and at least oneadditional rare earth element selected from among Pr, Nd, Dy and Tm,preferably Dy, as described in U.S. Pat. No. 5,376,303.

Preference is given to using phosphors based on an alkaline earth metalaluminate, in particular the phosphors described in EP-B-0 622 440, EP-A0 710 709, DE-A 195 21 119 and U.S. Pat. No. 5 376 303.

The amount of phosphor used is not restricted in any particular way, butfor economic reasons is generally up to about 50% by weight, based onthe total weight of the laminar body. The lower limit for the amount ofphosphor is determined, in particular, by the desired phosphorescentintensity and can accordingly be varied within wide ranges depending onthe application.

The present invention also provides a process for producing theabove-described laminar body, which process comprises the followingsteps: application of at least one layer containing an enamel to one orboth sides of a substrate and firing the applied layer or layerscontaining an enamel, characterized in that this layer or layerscontains/contain at least one phosphor.

The application and firing of the enamel is carried out by conventionalmethods known from the prior art. Thus, the enamel is applied in theform of an aqueous suspension (enamel slip) or as fine powder to thesubstrate, for example a generally degreased and passivated foil ofaluminum or aluminum alloy, with the aid of an application apparatus,e.g. a spray gun, and is subsequently fired at temperatures of fromabout 500 to about 600° C. When using a plurality of enamel layers,these are generally applied in succession and fired together.

The laminar body of the invention can then at any time be applied to asuitable support material, preferably a noncombustible support material,e.g. a metal plate, by adhesive bonding or welding, or else be applieddirectly to the article to be marked, likewise by adhesive bonding ormechanical fastening, e.g. riveting, clamping or screwing.

In a further, preferred embodiment, the layer containing an enamel andat least one phosphor can be applied by means of screen printing orother printing processes, transfers, templates, spraying with templatesor manual inscription.

In addition, the present invention also provides for the use of alaminar body as described above or a laminar body produced as definedabove to give an article phosphorescent properties, and also providesphosphorescent articles characterized in that they are provided withsuch a laminar body.

Examples of articles which are preferably provided in the context of thepresent invention with the laminar body of the invention are measuringinstruments, clockfaces, safety signs, keys, safety railings, helmets,any type of markings such as ones in or on lifts or as traffic signs,electric switches, writing instruments, toys or household appliances andsports equipment.

Furthermore, the present invention in its most general form provides forthe use of a phosphor to provide a laminar body comprising a substrateand, applied thereto on one or both sides, at least one layer containingan enamel with phosphorescent properties.

The present invention will be illustrated below with the aid of someexamples.

EXAMPLE 1

In a continuously operating unit, an aluminum foil having a thickness.of 80 μm was wound off a roll and ran through two degreasing baths, arinsing bath and a passivation bath and was subsequently dried.

A white enamel was subsequently applied in a thickness of about 60 μm toboth sides by means of spray guns, dried and fired.

An aluminum enamel slip to which a europium-dysprosium-doped strontiumaluminate (Lumilux® Grün SN from Riedel-de Haën) had been added asphosphor in an amount of 40% by weight, based on the enamel, was thenapplied and this enamel coating was dried and continuously fired. Thefoil was then again wound up onto a roll.

In subsequent use, appropriate lengths were wound off this roll and useddirectly.

EXAMPLE 2

An aluminum foil having a thickness of 100 μm, which already had awhitish colour as a result of embedding of TiO₂, was first pretreatedanodically and subsequently, while hanging free, coated on the reverseside with a waste aluminum enamel and on the front side with an enamelslip to which a phosphor as in Example 1 had been added and the enamelwas subsequently dried and fired. The thickness of the enamel layerobtained was 150 μm.

EXAMPLE 3

A 3 mm thick sheet of the aluminum alloy AlFeSi was degreased withalkali, then rinsed with demineralized water and dried. A slip was thenprepared according to the following formulation:

100 parts of aluminum frit

15 parts of floating agent

40 parts of water

12 parts of TiO₂

This slip was applied to the aluminum alloy sheet by spraying, dried andfired at 570° C.

Subsequently, a further slip was prepared according to the followingformulation:

100 parts of aluminum frit

30 parts of floating agent

60 parts of water

200 parts of phosphorescent pigment

This slip was processed in the same way as described above.

EXAMPLE 4

A body made of a sand casting alloy was degreased with alkali, rinsed anumber of times and passivated using HNO₃, and then dried. This body wascoated with a white slip as in Example 3 and fired. A slip was thenprepared according to the following formulation:

100 parts of aluminum frit

60 parts of water

25 parts of floating agent

250 parts of phosphor

This slip was dried, pulverized, dusted onto the casting and fired.

What is claimed is:
 1. A laminar body comprising a substrate whichcontains aluminum or aluminum alloy and, applied to said substrate on atleast one side, at least one layer containing an enamel, said at leastone layer containing an enamel containing at least one phosphorcomprising an alkaline earth metal aluminate.
 2. A laminar bodycomprising: a substrate comprising a perforated metal sheet having athickness of from 0.2 to 2.5 mm or a foil having a thickness of from 50to 500 μm and, applied thereto on at least one side, at least one layercontaining an enamel, said at least one layer containing an enamelcontaining at least one phosphor comprising an alkaline earth metalaluminate.
 3. A laminar body comprising a substrate and, applied theretoon at least one side, at least one layer containing an enamel, said atleast one layer containing an enamel containing at least one phosphorcomprising an alkaline earth metal aluminate, wherein each of said atleast one layer containing an enamel has a thickness of 400 μm or less.4. A laminar body comprising: a substrate; at least one layer applied tothe substrate, said at least one layer containing an enamel containingat least one phosphor comprising an alkaline earth metal aluminate; anda reflective layer of a white or light-coloured enamel having areflectance of at least 78% on at least one side of the body.
 5. Amethod for providing a phosphorescent article comprising the step ofcontacting an article with a laminar body according to claim
 1. 6. Amethod for providing a phosphorescent article comprising the step ofcontacting an article with a laminar body according to claim
 2. 7. Amethod for providing a phosphorescent article comprising the step ofcontacting an article with a laminar body according to claim
 3. 8. Amethod for providing a phosphorescent article comprising the step ofcontacting an article with a laminar body according to claim 4.